Fact Sheet 4.16. Forest Harvest Quantity and Timing

Harvesting is the procedure by which a forest stand is logged, with an emphasis
on meeting logging requirements and attaining silvicultural objectives. Harvest
scheduling is a process for allocating cutting and other silvicultural treatments
over a forest, with the emphasis on which treatments to apply as well as where
and when to apply them. The practice relates to when and how harvesting is done
(e.g., thinnings, including pre-commercial thinnings; selection; or clear-cut
harvests) and the timber volume extracted.

Use and Potential
Harvest intensity affects the quantity and quality of timber produced. The carbon
impact is directly connected to the end use of the wood products. For example,
increasing the rotation time, lengthening the period between harvest operations,
or reducing the volume extracted may lead to reduced growth rates and reduced
carbon sequestration in the forest, as well as producing less wood for bioenergy
or for replacing energy-intensive products such as steel, aluminum, plaster
board, and concrete.

Burschel et al. (1993) calculated that longer rotation periods could
increase carbon stocks in Germany by 0.7-1.8 Mt C yr-1 in the first 20 years
but would have adverse effects (on industrial roundwood productivity and carbon
sequestration) if further extended because of higher risk of natural damages.
For forests in Russia and the northwestern United States, intensive management
reduces forest carbon stocks below the levels found in native forests, whereas
increasing rotation lengths, retaining live trees through harvests, and decreasing
site disturbance related to harvest and regeneration can substantially increase
forest carbon stock (Krankina and Harmon, 1994; Krankina et al., 1996).
These two studies did not consider the end-use aspects, however. Several authors
have studied the impact on carbon sequestration (e.g., Plantinga and Birdsey,
1994; Boscola and Buongiorno, 1997; Boscola et al., 1997; Hoen and Solberg,
1997); the conclusion is that including the benefit of carbon will encourage
the rotation age to increase.

Forest growth studies have shown that the impact of different thinning practices
on total growth (and carbon sequestration) is insignificant in Germany (Strich,
1998). Row (1996) found that a thinning regime produces lower total carbon stocks
in a 50-year Loblolly pine rotation than thinned stands; Lunnan et al.
(1991) came to the same conclusion regarding lengthening the rotation periods
when studied at the stand level. In addition, the decrease in timber supply
caused by increased rotation length may shift the demand for timber to other
stands that will be harvested instead-creating a high probability of leakage.

Optimal thinning and clear-felling times (and quantities) are interlinked and
depend on other forest management measures (e.g., fertilization or plant density)
and objectives. Hoen and Solberg (1994) carried out one of the few studies that
analyzes thinnings, clear-fellings, and other silviculture measures (e.g., fertilization,
types and intensity of regeneration) simultaneously for a boreal forest region,
keeping harvest levels constant and maximizing carbon storage (including the
end use and decay of wood products) for the region over a long period. The study
illustrates that thinning and clear-felling times will be significant and will
complement each other. For example, thinnings on good site classes substitute
for clear-fellings on low site classes that have high standing volumes (but
low annual growth and carbon sequestration potential if harvested). Boscola
et al. (1997) show that the combination of harvest cycles and minimum
cutting diameters can maximize carbon sequestration, at costs of US$1.2 t-1
C sequestered, for an increase in cutting cycles from 40 to 50 years in lowland
tropical rain forest in Malaysia.

Associated Impacts
This practice could have positive and negative environmental benefits regarding
biodiversity, recreation, and landscape management, depending on local circumstances.
The main barriers are the lack of incentives, including the risk of negative
economic incentives.